To combat solar radiation, the skin has differentiated cells that are particularly suited to this function: the melanocytes. In the course of a complex process, melanogenesis, these cells manufacture melanin, a dark pigment which has the effect of protecting the skin structures and of increasing the time required to contract a solar erythema. However, not all melanins are protective. In particular, there exists one form of melanin, known as phaeomelanin, that is extremely phototoxic. Like all melanins, it is capable of reacting with certain forms of free radicals, but it can also cause the formation of free radicals that are even more toxic, and which are liable to cause irreversible damage to the genetic material of keratinocytes. Moreover, certain disorders associated with dysfunction of the melanization unit are liable to cause hyperpigmentation, which is occasionally particularly unsightly.
Thus, the use of melanin synthesis inhibitors is particularly advantageous in cosmetology, not only for applications in which true depigmentation is desired, as in the case of the bleaching of highly pigmented skin or the inhibition of hyperpigmentation in certain unaesthetic aspects, for example, but also for applications for lightening the complexion and for giving luminosity to the skin and radiance to the surface tissues. This inhibition of melanin synthesis may also be particularly advantageous in the context of therapeutic treatment for treating a true pathology.
para-Coumaric or para-hydroxycinnamic acids have been described as inhibitors of melanin production in numerous studies. However, these substances do not make it possible to obtain significant inhibitory effects on melanin synthesis. This excessively weak activity does not make it possible to obtain strong enough effects and these substances are thus little used in cosmetic or pharmaceutical topical applications for effectively combating unsightly pigmentations.
The prior art mentions in particular the use of vitamin C (or derivatives thereof) or kojic acid (or derivatives thereof) for inhibiting tyrosinase, but these molecules are either cytotoxic at the concentration used, or of little efficacy. It is known practice in particular to use ferulic acid or caffeic acid as depigmenting agent in cosmetic compositions. However, these compositions are not entirely satisfactory as regards the efficacy of the depigmenting action.
Thus, an aim of the present invention is essentially to solve the technical problem that consists in providing a depigmenting agent that is more active than those currently used, such as caffeic acid or ferulic acid.
Another aim of the present invention is also to provide compositions using these depigmenting agents, cosmetic care methods and/or pharmaceutical treatment methods using these depigmenting agents, and also the use of these depigmenting agents to exert antiradical and/or antiinflammatory activity.
A further aim of the present invention is also to provide compositions whose active compounds are extracted from plants.
Yet a further aim of the present invention is also to provide compositions that can be applied topically.
An additional aim of the present invention is also to provide depigmenting agents for combating skin hyperpigmentation, especially for aesthetic purposes, mainly when the skin has at least one hyperpigmented localized area.
A further aim of the present invention is to solve the technical problems mentioned above in a safe and reliable way and especially while avoiding undesirable side effects, particularly in human beings, for example by reducing the cytotoxicity of the active agents used.